Drinking water in Yarmouth and North Yarmouth tested positive for coliform bacteria last month, but the untreated well water poses no health threat to customers, Yarmouth Water District officials said Friday.

Bacteria was found in water samples taken at two locations: the Community House on East Main Street in Yarmouth and the 200,000-gallon water tank on Delwin Drive in North Yarmouth, said Christopher Curtis, the district’s assistant superintendent.

Follow-up samples at both locations have tested negative for bacteria, Curtis said. However, the district drained and refilled the tank in North Yarmouth as a precaution.

The district does monthly bacteria tests at eight locations in the system and must notify the public within 30 days if more than one location tests positive in one month, Curtis said. The district ran a public notice in Friday’s Portland Press Herald.

Curtis said this summer’s hot weather likely caused bacteria to grow in the tank in North Yarmouth, which is partly above ground. The tank also has little water turnover because it serves only 375 homes and businesses, which draw a total of about 30 gallons per minute.

“Draining and refilling the tank reduced the water temperature by seven degrees, which is significant for that amount of water,” Curtis said.

The North Yarmouth tank is one of three in the district, which serves nearly 3,000 rate payers in Yarmouth and North Yarmouth. The tank has two sections, so no customers went without water when it was drained during a week early last month.

Established in 1895, the district draws water from four wells in North Yarmouth. The water is clean enough to meet federal drinking water standards without chlorination, Curtis said.

However, the district does occasionally shock the system with chlorine, and when it does, some residents call to complain about it, Curtis said. It has been more than a year since the last chlorine treatment.

The coliform bacteria test is very sensitive and can give false-positive results, Curtis said. The test also identifies fecal coliform bacteria, which weren’t present in the tests in August, he said.

Coliforms are a group of bacteria — most of them harmless — that are found in soil, plant material and the digestive tracts of animals and humans, according to the U.S. Environmental Protection Agency.

Fecal coliforms, including E. coli, are associated with fresh feces and indicate the presence of disease-causing agents. Contaminated water can cause diarrhea, cramps, nausea and vomiting.

If fecal coliform had been found in Yarmouth and North Yarmouth, Curtis said, the district would have announced a public emergency, directed customers to boil water and taken steps to identify and correct the source of contamination.

Staff Writer Kelley Bouchard can be contacted at 791-6328 or at:

kbouchard@pressherald.com